Cell-free hemoglobin can be measured in the plasma of patients with sickle cell anemia, hemodialysis, after red blood cell transfusion, and in patients with sepsis. Cell-free hemoglobin in these patient population has been associated with poor outcomes, including an association with an increased risk of death. Acetaminophen may have a protective effect in these patient populations by inhibiting hemoprotein-mediated lipid peroxidation. The purpose of the present trial is to study the effect of acetaminophen on lipid peroxidation in adults with severe sepsis and detectable cell-free hemoglobin.